1. Field of the Invention
The present invention relates to an ink jet recording apparatus and an ink jet recording head which is applicable to the apparatus, and more particularly to a thermal energy generating element in the recording head and a wiring structure of the head.
Here, it should be construed that a word "recording" means a technical concept of applying ink to all kinds of recording mediums each adapted to receive ink from the ink jet recording head, e.g., cloth, thread, paper and various kind of sheet-shaped material, or of performing the ink application independently on meaning of an image to be recorded. Further, it should be construed that a word "recording apparatus" includes a technical concept defined by various kinds of information processing apparatuses and a printer serving as an outputting unit for the information processing apparatuses. The present invention can be applied to each of the above apparatuses tor practical use ot the latter.
2. Description of the Prior Art
A recording apparatus having a function of serving as a printer, a copying machine, a facsimile and so forth or a recording apparatus operable as an outputting unit for complex type electronic equipment and a work station such as a computer, a word. processor and so forth is constructed such that an image is recorded on a recording medium in conformity with image information. For example, an ink jet recording system has been hitherto known as one of recording systems usable for the apparatuses as mentioned above. The ink jet recording system makes it possible to record an image on a recording medium with more excellent fineness than any other type of recording system. For this reason, attention has been hitherto paid to the ink jet recording system in additional consideration of a possibility that each recording operation can be performed at a comparatively high speed while generating a low intensity of noisy sound.
As is heretofore known in the art, an ink jet recording head usable for practicing the ink jet recording system (hereinafter referred to simply as a recording head) is constructed such that a plurality of square or rectangular heaters (each serving as a thermal energy generating element) are arranged on a substrate (device substrate) made of silicon, wiring is electrically connected to each heater, and moreover, an ink flow path is formed for each of the heaters on the base plate. In this case, the recording head may be constructed such that a plurality of heaters are arranged in the vicinity of one end edge of the base plate and the foregoing one end edge of the base plate constitutes a part of a face of the discharging portion. Each wiring is electrically connected to the individual heater. The heater is driven by supplying a driving signal through the wiring thereto.
With such construction, however, as the number of heaters is increased, the number of the wirings is also increased by two times as that of the heaters. Therefore, a width of cach wiring must be unavoidably reduced as the number of heater is increased. There is fear that this leads to inconveniences that a value of resistance in the wiring range is increased, resulting in a quantity of electricity loss being correspondingly increased, and moreover, the temperature of the recording head is undesirably elevated, causing properties of the recording head to change disadvantageously.
In order to solve such problems, a method for reducing the number of the wiring to about a half is used, the method comprising a common wiring for connecting commonly the heaters to one another.
In the ink jet recording head, pulse-like electric current is applied to a plurality of heaters for a period of several .mu. seconds, causing ink to be discharged from the recording head by bubbles generated in ink by the heaters. Therefore, since an intensity of electric current, which flows instantaneously through the heater, is very high, there is fear that the intensity of driving electric current to be applied to each heater varies corresponding to image to be recorded due to resistance of wiring with the concentration of electric current when a common wiring is used for the heaters.
To cope with the foregoing inconveniences, Japanese Patent Application Laid-open No.208251/1985 (1985) discloses a method to be practiced such that a plurality of nozzles and ink flow paths are divided into a plurality of blocks, adjacent nozzles are assigned to different blocks, each block is driven at a different timing so as not to allow adjacent nozzles to be simultaneously driven, and common electrodes of two or three heaters are electrically connected to each other via a single wiring.
With the construction disclosed in the above publication, the number of the wirings can be reduced to three or four, and there is no fear to cause the problem described above regarding the concentration of the electric current because the number of the wiring is numerous.
However, with such construction, when a central axis of the heater substantially coincides with that of the nozzle like usual ink jet recording head, a pitch defined between one nozzle and another nozzle adjacent thereto is not equal. It causes the complex problem on the head structure that a plurality of nozzle arrays must be arranged in order to compensate the formation of a wide-pitch portion.
Furthermore, with the above arrangement of heaters, when only the nozzle pitch is equal, the coincidence between the central axis of the nozzle and that of the heater is largely off. There is fear that an excellent recording image cannot be obtained because the ink discharge in each nozzle is uneven.
On the other hand, in the conventional recording head, an intensity of kinetic energy owned by each ink droplet discharged from the recording head is held merely at a level of about 1/10000 of electric energy applied to each heater, resulting that an energy efficiency is not very high. This is attributable to the fact that a large amount of ink is caused to move in each nozzle without any contribution to ink discharge.
To improve a thermal energy converting efficiency, it is inevitably necessary that the nozzle structure is designed in an optimum manner. For example, in the case of a recording head of the type adapted to discharge ink in the direction substantially along a face of the device substrate on which the heater is arranged, it is possible to reduce an amount of ink which does not contribute to ink discharge, i.e., to reduce an amount of ink which is not practically discharged from the recording head on receipt of thermal energy by shortening the distance as measured from a heater to an ink discharge nozzle so as to allow an amount of ink filled in an ink flow path extending therebetween to be minimized. Also in this case, the recording head may be constructed such that gas bubbles generated in ink by the heaters are exhausted to the outside via the ink discharge nozzle.
However, when the distance between a heater and an ink discharging nozzle is intentionally shortened in that way, it becomes difficult from the viewpoint of a space to be occupied that a connection wiring portion for electrically connecting electrodes for a plurality of heaters to each other on the common basis is disposed between the heater and the ink discharge orifice. In this case, when a wiring between the heater and the discharge portion is reduced, a resistance in the wiring range is increased. When a high accuracy production apparatus such as a mask-aligner or a similar apparatus is employed because of the necessity for forming a fine wiring structure, there appears a drawback that the recording head is produced at an increased cost. The conventional wiring structure is preferably employable in the case that electric current is caused to flow in parallel with the direction of ink discharge, and is suitably employable in the case that heaters each having a long contour as seen in the direction of ink discharge are driven for the recording head. However, the conventional one is unsuitable in the case that heaters each having a long contour in the direction rectangular to the direction of ink discharge are driven for the recording head.
In the latter, when electric current is caused to flow in parallel with the direction of ink discharge, resistance of each heater is reduced compared with the former. Thus, there arises a necessity for allowing a high intensity of electric current to flow in order to drive the recording head at the same electric power as the conventional one. However, this leads to the result that the electric power loss induced by wiring resistance is undesirably increased.